Beijing has announced it will add 50 miles of subway track by the end of next year, making the city's subway system bigger than New York's. But will the new additions alleviate the city's notorious traffic and pollution?

Just five years ago, the Beijing subway system was 70 miles long. Today it’s nearly four times that. But economics professor Zhao Jian at Beijing’s Jiaotong University says it’s going to take more than hundreds of miles of subway lines to solve Beijing’s traffic problem.

"The key to alleviating traffic and pollution in Beijing is to raise the cost of owning and using cars," says Zhao. "As it stands, parking fees are very low and traffic tickets aren’t that expensive. This needs to change."

In Shanghai, on the other hand, a license plate typically costs as much as the car itself. And that’s meant Shanghai, which has a bigger, more affluent population than Beijing, has half as many cars and is often spared Beijing’s persistent toxic haze.